A conventional speed measuring apparatus for measuring a speed of a moving member comprises a first set of a first infrared ray photoelectric tube and a first infrared ray projector, and a second set of a second infrared ray photoelectric tube and a second infrared ray projector. The first and second infrared ray photoelectric tubes are placed on a side of a road. The first and second infrared ray projectors are placed on the other side of the road in opposition to the first and second infrared ray photoelectric tubes, respectively. The first and second sets are positioned along the road with a predetermined interval of, for instance, 7 m. First and second infrared rays are projected from the first and second infrared ray projectors to the first and second infrared ray photoelectric tubes, respectively.
When an auto car moves on the road, the auto car interrupts the first and second infrared rays, respectively. The conventional speed measuring apparatus measures a time period from the interruption of the first infrared rays to that of the second infrared rays to measure a speed of the auto car by using an oscillating circuit having a CR oscillator or a quartz oscillator.
However, the conventional speed measuring apparatus for measuring a speed of a moving member by using a general purpose quartz oscillator has disadvantages in that it can not measure a speed with higher precision than an unit of 1/10 second.
Further, the conventional speed measuring apparatus for measuring a speed of a moving member by using a special purpose quartz oscillator has disadvantages in that its cost is high to measure a speed with higher precision than an unit of 1/100 second, because a quartz oscillator which has a high oscillation frequency is expensive.
Even further, the conventional speed measuring apparatus for measuring a speed of a moving member by using a CR oscillator has disadvantages in that it can not measure correctly a speed, because the precision of the CR oscillator is affected in accordance with fluctuations of the temperature and the humidity.
Further, the conventional speed measuring apparatus for measuring a speed of a moving member has disadvantages in that it can not be used as a speed measuring toy, because it is hard to miniaturize the conventional speed measuring apparatus which has the first and second sets of the infrared ray projectors and the infrared ray photoelectric tubes to be positioned with a predetermined interval of, for instance, 7 m.